Engine starter



10, 1 931. M. P. WHITNEY 3 3 0 ENGINE STARTER Filed July l5, 192" 5 Sheets-Sheet 1 March 10, 1931. v M, N Y I 1,795,460

ENGINE STARTER iled July 15. 1927 3 Sheets-Sheet 2 Patented Mar. 10, 1931 UNITED STATES PATENT OFFICE MAURICE P. WHITNEY, OF ELMIRA, NEW YORK, ASSIGNOR TO ECLIPSE MACHINE COMPANY, OF ELMIRA, NEW YORK, .A CORPORATION OF NEW YORK ENGINE STARTER Application filed July 15, 1927; Serial No. 205,901.

tion is an improvement upon the usual form of the Bendix drive such as exemplified in Bendix Patent No. 1,125,935 issued on J anuairy 26, 1915, and the object thereof is to provide a screw shaft and pinion or driving member with screwthreads of a special and improved formation in order to attain the results and advantages hereinafter made apparent.

" In the drawings Figure 1 is a sectional elevation of a drive embodying my invention;

Fig. 2 is a detail elevation on a somewhat larger scale of a portion of the screw shaft; Fig. 3 is a cross section of the driving member or pinion; 7

Fig. 4 is a sectional elevation much enlarged illustrating the screw threaded portion of the screw shaft and the pinion; and

Fig. 5 is a sectional elevation similar to Fig. 4 except that the pinion is in mesh with the flywheel.

In Fig. 1 I have illustrated a drive which is the same as the regular Bendix drive with the exception of the new formation of the threads of the screw shaft and the driving member or pinion. T his-construction briefly described comprises a screw shaft 1 which as herein shown is mounted upon the extended armature shaft 2 of the prime mover or electric motor-3. This shaft is drivingly connected by means of the drive spring 4 with a driving head 5-which is secured to such armature shaft. The pinion 6 is threaded upon the screw shaft for longitudinal movement thereof and rotary movement therewith. When it is in cranking position as shown in Fig. 1 it bears against a stop nut 7 screwed and secured to the outer end of the screw shaft. At this time the pinion is in mesh with the teeth 8 of the engine member or flywheel 9. The drive illustrated inFig. 1 is of the outboard type inasmuch as it has a bearing 10 at its outen end and-the pinion 5 moves outwardly.- to cranking position, but

it will be understood that my invention is equally applicable to the inboard type in which the pinion moves inwardly toward the motor to cranking position. It will also be understood that my invention relates to the formation of the threads of the screw shaft and pinion of an engine starter and that therefore the construction of the associated parts is not material.

In the usual Bendix drive both sides of the threads are cut with an angle which is symmetrical with relation to a radial line from the axis of the screw shaft and its pinion. In the present instance, and referring particularly to the screw shaft threads which are of the triple type, the non-pressure side of such threads which is indicated at 11 is formed with a single surface. If a longitudinal section were to be taken through the shaft along its longitudinal axis such section would show that the non-pressure side of this thread was cut with approximately a 45 degree angle which is the practical and preferred angle.

' The other or pressure side of these threads is formed with two angles. that portion nearest the root diameter indicated at 12 being almost a square thread and the same in practice and for manufacturing purposes being cut or formed approximately at an angle of 5 degrees from the vertical. The top portion of the threads on this pressure side, that is the outer corners are formed or beveled at an angle which by preference and in practice is an angle of 45 degrees to the vertical. This latter angle or bevel is indicated at 13.

\Vhile the threads of the screw shaft are continuous they are made differently in two zones or sections, the dividing line between these zones being indicated by the cross dotted line 14 in Fig. 2. The threads in the left hand zone (Fig. 2) are made of a certain diameter, but the threads in the other or right-hand zone are made of a lesser diameter as indicated by the particular threads 15. These threads are reduced in diameter by the removal of that portion of the original threads which would. be beyond the bevel portion. 13. As a. result these threads in the right hand zone have no bevel portion 13 on their pressure sides but merely the substantially flat or straight portion 12.

The pinion has its bore provided with screw threads corresponding with the shaft threads of the left hand zone thereof and therefore such pinion threads have a. substantially straight surface 16 cooperating with the surface 12 of the shaft'threads and an inclined or bevel surface 17 to cooperate with the bevel surface 13 of the shaft threads. These pinion threads also have the inclined surface 18 c0- operating with the correspondingly inclined surface 11 of the shaft threads.

Describing generally the operation of the drive and particularly the functioning of the new formation of screw threads, and starting with the parts in the cranking position of the pinion as shown in Fig. 1, the direction of rotation ofthe. screw shaft is indicated by the arrow and the torque is transmit-ted from the starting motor through the drive head 5, drive spring 4, screw shaft or sleeve 1 and pinion 6 to the flywheel. The torque from the starting motor gives by means of the screw threads a longitudinal component to the pinion. This component is resisted by the stop nut 7 by means of its flat or perpendicular face 19 positioned against the correspondingly flat or perpendicular ends 20 of the triple shaft threads. Due to the lead of the shaft threads a variation in the coeflicient of friction between the threads in the pinion and on the screw shaft might possibly give a condition which would cause the pinion to stick on the shaft threads in which case the starting of the engine would cause the motor armature to be driven at an excessive rate of speed which would be liable to destroy the armature windings. Any tendency for sticking between the pinion and screw shaft is materially reduced by making the angle of the pressure side such that it is or approaches a square thread as indicated at 12 so that the longitudinal component will not cause sticking. The back end of the pinion is preferably counterbored as shown at 21 so that when the pinion is in its driving or cranking position against the stop nut and in mesh with the flywheel, the only contact between the threads of the pinion and the screw shaft is against av thread with a side which is nearly vertical or straight, that is the side indicated at 12.

' In the normal operation of the drive when the pinion meshes with the flywheel correct registry between the pinion teeth and the flywheel teeth does not always occur in the longitudinal movement of the pinion. In order to insure mesh of'the pinion with the flywheel in case of end to end abutment between the pinion teeth and the flywheel teeth, it is necessary that the pinion rotates slightly with the screw shaft to the end that the proper registry for mesh may be obtained. When this condition of abutting occurs as is illustrated in Fig. 4 the continued rotation of the motor armature causes the screw shaft 1 to screw back through the pinion against the compression of the drive spring 4:. As this shaft moves back the compression'of the spring gradually increases due to the longitudinal component between the threads of the screw shaft and the pinion. The same pressure of course is maintained between the ends of the pinion teeth and the flywheel teeth, and between the threads of the screw shaft and pinion. Due to the rather loose fit of thethreads between the pinion and the screw shaft it is possible for the pinion to cock slightly on such shaft. Consequently the axis of the pinion and the axis of the a screw shaft will not exactly coincide but the pinion axis will assume the position as shown by the dotted line XY in Fig. 4. This cock ing action causes a portion of the pinion thread. such as indicated at 17. to contact the similar portion or surface 13 of the shaft threads. Due to the cooking action of the pinion the threads thereof on its lower portion and as to its non-pressure side 18 will be in contact with the corresponding non-pressure side 11 of the shaft threads so that the pinion will be riding against surfaces which are cut on the described angle which is preferably one of 45 degrees. Due to the longitudinal pressure caused by the rotation of the screw shaft through the now stationary pinion, a clutching effect of the pinion on the screw threads is obtained which transmits sufficient torque from the screw shaft to the pinion to carry the abutting pinion tooth past the flywheel tooth against which it abuts, thereby giving proper registry between the pinion and the flywheel. The drive spring is then released from its compression load and moves the assembly of screw shaft, pinion and stop nut in a forward direction. The pinion is then carried into complete engagement with the engine flywheel until it comes into contact with the stop nut 7 and continued rotation of the starting motor is thus transmitted to the engine flywheel for cranking the engine.

The division between the two zones of the shaft threads is so located that when end to end abutment occurs between the pinion and the flywheel teeth the pinion is then in the left hand zone and thereby cooperates with shaft threads having a very large angle with reference to a radial or vertical line which gives more effective wedging or jamming effect between the pinion and screw shaft, thereby causing the pinion to rotate/with such shaft in the manner above explain ed.

After the engine starts under its own power, the pinion is demeshed in the usual manner and when the pinion moves back on the shaft threads the non-pressure sides thereof are used and under the present construction this is a continuous surface whether the pinion is in driving relationship or in a completely delneshed position. As the pinion moves back out of mesh with the flywheel it has a tendency to cock in the same manner down so that it will assume the same speed of rotation as the screw shaft and prevent the pinion from being thrown back violently against the heel of the shaft threads, thereby preventing damage to the ends of the threads in both the pinion and screw shaft. Due to the peculiar thread construction a smaller pinion counterweight can be used than in the regular form of standard Bendix drive inas much as the angle on the side of the thread is so great that more of a binding action is obtained, thereby permitting a decrease in the size of such counterweight.

At 231 have shown an anti-creeper means for the pinion such as exemplified by Van Ness Patent No, 1,375,870 issued on April 26, 1921. ihis form of device is preferable in connection with this particular formation of screw threads in view of the fact that the land on the top of these threads is rather narrow and difficulty might be'experienced in using the ordinary form of anti-creeper device or drift pin which has to ride properly on top of the threads.

I claim:

1.v An engine starter drive including a shaft having screw threads, and a pinion threaded thereon, the threads on that section of the shaft occupied by the pinion when in cranking positicn being of less diameter than the threads on the other section and being formed on their pressure sides at approximately right angles to the axis of the shaft, and the pinion threads being complelnentally formed on their pressure sides throughout that portion of their depth which cooperates with said smaller-diameter shaft-threads.

52. An engine starter drive including a shaft having screw threads, and a pinion threaded thereon, said screw threads being formed on their pressure sides at approximateiy right angles to the axis of the shaft and that section of the threads occupied by the pinion when in cranking position being of less diameter than the other section.

3. An. engine starter drive including a shaft having screw threads, and a pinion threaded thereon for automatic return after engine-starting, said screw threads being formed on their pressure sides at approximately right angles to the axis of the shaft and being formed on their non-pressure sides at an angle materially less than a right angle to the axis of the shaft.

4. An engine starter drive including a shaft having screw threads, and a pinion threaded thereon for automatic return after engine-starting, said screw threads being formed on their pressure sides at approximately right angles to the axis of the shaft and being formed on their non-pressure sldcs at an angle of approximately as hereinbefore explained only in this case by reason of the counterweight 22 of the pinion. This cocking action tends to slow the pinion 5. An engine starter drive including a shaft having screw threads, and a pinion threaded thereon, said screw threads being formed on their pressure sides at approximately right angles to the axis of the shaft and having the outer corners on such pressure sides cut away.

6. An engine starter drive including a shaft having screw threads, and a pinion threaded thereon, said screw threads being formed on their pressure sides at approximately right angles to the axis of the shaft and having the outer corners on such pressure sides beveled off at an angle of approximately 45 to the plane of such sides.

7. An engine starter drive including a shaft having screw threads, and a pinion threaded thereon, such threads being continuous but having two zones of differently 8. An engine starter drive including a shaft-having screw threads, and a pinion threaded thereon, such threads being continuous but having two zones of differently formed threads, the threads of the first zone, occupied by the pinion when in cranking position, being of less diameter than those of the second zone and all the threads having pressure sides which are formed at approximately right angles to the axis of the shaft to minimize sticking tendency, the bore of the pinion having threads which cooperate with the threads of both said zones but which correspond in formation with the threads of said first zone.

9. An engine starter drive including a shaft having screw threads, and a pinion threaded thereon, said threads being formed on their pressure sides at approximately right angles to the axis of the shaft and having their outer corners on such side beveled off, and the pinion having a bore with threads having pressure sides corresponding in formation with those of the shaft threads.

10. An engine starter drive for automatic T demeshing of the pinion, including a shaft side'of the shaft threads of said driving zonebeing foiined for coaction with the pinionthreads at an angle appropriate for nonsticking and the non-pressure side ofasaid.

shaft-threads of the non-driving zone"being formed for coaction with said pinion-threads at an angle more conducive to binding.

11. An engine-starter drive for automatic mesh-insurance and automatic demeshing of the pinion, including a shaft having screwthreads presenting a driving zone and a non- 5 driving zone, the pressure side of the shaft threads of said driving zone being formed for coaction, with the pinion-threads at an angle efiectively different from the angle at which a pressure-side portion of said shaft- 19 threads of said non-driving zone are formed to coact with said pinion-threads.

12. An engine-starter drive for automatic mesh-insurance and automatic demeshing of the pinion, including a shaft havin'g screw threads presenting a driving zone and a nondriving zone to be occupied by the pinion in driving and non-driving positions respectively, and a screw-threaded pinion on said shaft, the pressure side of the shaft-threads 20 of said driving zone being formed for coaction with the pinion-threads at an angle mininiizing sticking and both sides of said shaftthreads of the non-driving zone being formed for coaction with said pinion-threads at an angle more conducive to binding.

13. An engine-starter drive for automatic ineshdnsurance of the pinion, including a shaft having screw-threads presenting a driving zone and a non-driving zone to be so occupied by the pinion in driving and nondriving positions, respectively, the pressure side of said threads of said non-driving zone being formed at approximately right angles to the axis of the shaft adjacent their bases and more acute angle to the shaft-axis near their tops, and the threads of said driving zone being of smaller diameter than those of the non-driving zone and having pressuresides formed at said first-mentioned angle to 46 the axis of the shaft; and a screw-threaded pinion having threads which cooperate with the threads of both said zones but with pressure sides corresponding in formation with the shaft-threads of the non-driving zone.

In testimony whereof, I have subscribed my name.

MAURICE P. RVHITNEY. 

